1. Field of the Invention
This invention relates to an apparatus and process for etching fluoroplastics.
2. Description of Prior Art
Fluoroplastics are a class of parrafinic polymers which have some or all of the hydrogen replaced by fluorine. These materials are defined by the American Society for Testing and Materials (ASTM) as plastics based upon polymers from monomers containing one or more atoms of fluorine or copolymers of such monomers with other monomers, the fluorine containing monomer(s) being present in the greatest amount by mass (ASTM D833). Fluoroplastics are made by free radical initiated polymerization or copolymerization of the monomers. Fluorocarbon plastics, those made from perfluoro monomers, include polytetrafluoroethylene (PTFE), fluorinated ethylene-propylene copolymer (FEP), and perfluoroalkoxy resin (PFA). Other fluoroplastics include ethylene-tetrafluoroethylene copolymer (ETFE), polyvinylidene fluoride (PVDF), polychlorotrifluoroethylene (PCTFE), ethylene-chlorotrifluoroethylene copolymer (ECTFE) and polyvinyl fluoride (PVF).
Fluoroplastics exhibit performance characteristics such as: resistance to harsh chemicals, a wide range of working temperatures (-300.degree. F. to 500.degree. F.), outstanding electrical insulation properties, low dielectric constants and high resistivity, and very good flame resistance. Fluoroplastics also have a low coefficient of friction giving them non-adhesive and self-lubricating surface qualities.
These non-adhesive properties are a disadvantage when it is necessary to bond fluoroplastics to other materials. In such cases, the surface of the fluoroplastic to be bonded must be treated or etched so that it can accept an adhesive. Fluoroplastics can be effectively etched with a solution of metallic sodium in anhydrous ammonia. The fluoroplastic is either dipped in the etchant solution, or, if it is not to be etched all over, etchant is applied only to the surfaces to be bonded while the other surfaces are protected from the etchant. In the case of fluoroplastic tapes or sheets, in general, only one side is etched.
A common method of etchant one side of a roll of fluoroplastic tape is to spray etchant onto a steel roller and then run the side of the tape to be etched, over the roller. This applies etchant to the underside of the tape. This method wastes a great deal of etchant. The ethcant loses potency when it is exposed to moisture in the air. Fresh etchant constantly must be applied to the roller. Moreover, one-inch wide strips, along both edges of the tape, must be scrapped with this method. This is due to etchant rolling over the edge of the tape and etching the outer edges of the tape on both sides.